The production of crude oil often requires the use of artificial lift means by which the crude oil is lifted from the bottom of the borehole to the surface of the ground. Downhole pumps of the reciprocatory type used downhole in a wellbore for lifting crude oil from the bottom of the well thousands of feet to the surface of the ground have been employed in the oil field for many years. These downhole pumps are manufactured by a large number of different firms and therefore the pumps take on a number of different forms.
The produced fluid being lifted from the production zone always has some compressible fluid, such as natural gas, solubilized therein. As the formation fluid migrates from the payzone, through the casing perforations, and into the pump intake, separation between the gaseous and liquid phase of the formation fluid often occurs. Sometimes the separation is negligible and can therefore be ignored, or at least tolerated; however, the separation of the gas and liquid in most wells is considerable and brings about a condition recognized in the oil field production art as "gas locking". Gas locking is more likely to occur as the fluid level at the bottom of the borehole is lowered due to the pumping action. This aspect of downhole pumping, or artificial lift devices, and its deleterious effect upon downhole equipment has been studied at great length.
Most downhole pumps used in conjunction with pumpjack units have a plunger attached to be reciprocated by a rod string. The plunger has a check valve assembly, called a traveling valve assembly, therein which controls the flow of formation fluid through the plunger on the downstroke, and which closes to enable the plunger to lift the fluid on the upstroke.
Other downhole pumps used in conjunction with pumpjack units have a barrel attached to the sucker rod string while the plunger remains stationary respective to the borehole. In this event, the reciprocating barrel, has a traveling valve assembly associated therewith which controls the flow of formation fluid through the barrel.
In either event, it is advantageous to insure the ball of the traveling valve assembly is lifted from its seat as the pump nears the end of the downstroke, thereby expelling any compressible fluids from the pump variable chamber and obviating gas locking. This should not be confused with "fluid pounding" which results from a pumped off condition, because nothing other than increased flow from the production formation can avoid pumping off a wellbore.
The patents to Simon U.S. Pat. No. 4,219,311; Ritchey U.S. Pat. No. 2,690,134; Patterson et al U.S. Pat. Nos. 2,344,786 and 2,344,787; Hall U.S. Pat. No. 2,132,161; Streich U.S. No. 1,685,650; Knotts et al U.S. Pat. No. 1,498,042; and Farrah U.S. Pat. No. 984,084 represent the pertinent prior art.
Ritchey '134 discloses a downhole pump having a traveling valve element 44 which is upset from its seat by a finger 36. Note cage 30 attached to fixed plunger assembly 12, 20, 24, 26.
Hall '161 shows rod 11 guided at 10 and interposed between balls 6 and 13. Hence, the rod 11 is spring loaded by the lower ball spring 5.
Knotts et al '042 discloses a finger movable against upper ball 7. Note the spring in FIG. 2 which biases the finger downhole.
Patterson et al '786 and '787 shows a downhole pump having a plunger 46 which is spring loaded and upsets upper ball 37.
None of the above patents show a pushrod attached to the traveling valve of a downhole pump and means for moving the push-rod towards the ball valve during the downstroke so that the ball is moved a limited amount that cannot cause damage to the ball cage and which exhausts compressible gases from the pump working chamber.
The various different solutions provided by the above prior art references are deemed unsatisfactory, either because of their great complexity and expense, or because of the inherent damage that can potentially result as a consequence of the mechanism not being properly adjusted as contemplated by the inventor. The employment of apparatus thousands of feet downhole in a borehole cannot be directly monitored and controlled once the apparatus is operating out of sight and accordingly, it would be desirable to have made available improvements in apparatus for preventing gas lock in downhole pumps which avoid damage to the valve cage of the pump in the event the apparatus and downhole pump are not precisely adjusted to the optimum that may be desired.